落马洞暗河发育特征及其洪涝成因分析

根据区域岩溶发育史分析认为,湖北宣恩县落马洞暗河的形成总体上可分为两个阶段:第一阶段发生在白垩纪末至晚第三纪。在该阶段中,降水主要通过发育于卧西坪岩溶坡立谷地两侧的小型洼地、落水洞汇入地下管道,往卧西坪谷地排泄,在卧西坪一带形成一小型岩溶湖泊的同时,还在谷地西侧形成了下黑槽、铜锣坪、扁洞三个近东西向地下暗河系统。第二个阶段发生在晚第三纪至今。在这一期间,随着区域构造运动的振荡性抬升,岩溶侵蚀基准面不断下降,在谷地内形成了上、下黑槽、铜锣坪落水洞与卧西坪消水洞等垂向岩溶管道,贯通早期形成的东西向管道并袭夺卧西坪和铜锣坪一带的地表岩溶湖水,使得原分散的岩溶水系统通过南北向的主管道集中排泄,形成了多进口的树枝状复杂管道暗河系统。卧西坪岩溶坡立谷内常年遭受洪涝的原因主要是由于落马洞地下暗河形成年代较晚,管道规模较小,且洞内坍塌淤积严重,排水能力小。在此基础上,提出了加强流域水土流失管理、疏通河道和新建排水隧洞等治理措施与防治对策。

Analysis on the development characteristic of the Luoma Cave Underground River and the origin of the flood

According to the karst development history in the region, the formation and development of the Luoma Cave Subterranean River can be divided into two stages. The first stage occurred from the end of the Cretaceous Period to the late Tertiary Period. In this phase, precipitation was caught into the karst under-ground pipeline through the small karst depression and sinkholes located by the sides of the Woxiping polje, then drained into Woxiping polje and formed a small karst lake, and 3 east-westwards underground rivers formed at the same time. The second phase occurred from the end of the Tertiary Period until now. During this stage, with the uplift of the regional oscillated structure motion, the erosion base level declined continually. The Xiaheicao, Tongluoping and Woxiping sinkholes formed, and the east-west wards pipelines that formed in the early phase were transfixed and then the new pipeline captured the water from the karst lake, which made the dispersive karst water system discharged focused through the south-north wards pipeline and formed multi-entrance dendritic underground river system. The scale of the Luoma Underground River which formed in the later periodis too small and highly filled up that led to the discharging capacity get diminished, which is the main causation of the flood disaster in the polje. Based on this analysis, the governing way of the flood disaster in the drainage basin should include enhancing management of soil erosion, dredge river way and build new drainage tunnel.